Field of the Invention
This invention relates to the art of powder metallurgy and more particularly, to Al-Cr alloys in which the content of Cr is limited within a certain range and a defined amount of Ti is also added with or without Fe. The alloys have well-balanced properties of a heat resistance, plastic workability and toughness.
Description of the Prior Art
Since Al alloys have a number of merits such as lightweight, good working properties and the like, wide utility as a substitute for iron in the fields of automobiles and aircrafts where lightweight is essentially required has been expected. For instance, in the field of automobile industries, there is the recent tendency that movable parts in a high temperature atmosphere, e.g. a connecting rod, are made light in weight so as to design an engine of a high performance. Accordingly, there is a strong demand for materials which are light in weight and high in strength for use as a substitute for iron.
However, known ingot metallurgy Al alloys (I/M alloys) are difficult to apply to parts which require high strength under high temperature atmospheric conditions such as, for example, various engine parts. With 2000 series alloys which are considerd to have the highest heat strength of the known I/M alloys, the strength is brought about mainly with the precipitation phase of Cu and Mg used as main additive elements. In a temperature range over 150.degree. C. in which the precipitation phase is made coarse, the alloys are abruptly softened, making it too difficult to use as a strength member.
In recent years, various types of Al-based alloys have been developed using rapid solidification technique (R.S.T.) in order to meet the requirements in various fields of industries. For instance, a molten Al alloy containing metallic elements such as Fe, Cr, Mn, Ni, Ti, Zr, V and the like is rapidly solidified into the form of fine pieces such as powder. When the powder is consolidated to a massive body by means of the powder metallurgy, the thermally stable compounds which comprise the above-mentioned metallic elements are finely dispersed in the Al matrix. Thus, a great improvement of the high temperature strength can be expected.
Up to now, extensive studies have been made on Al-Fe based powder-metallurgical alloys having high heat resistance, such as Al-Fe-Ce alloys. In very recent years, attention has been drawn to the high heat resistance of Al-Cr-based alloys as reported by L. Katgerman et al (P/M Aerospace Materials 12-14, November 1984).
Al-Cr-based alloys are described, for example, in U.S. Pat. No. 4033793 and Japanese Laid-open patent application No. 59-116352. The alloys set forth in these publications have, respectively, good characteristics properties or features.
However, in practical applications, this type of alloy should have not only a heat resistance or heat strength, but also good plastic workability and high toughness. For example, when these alloys are applied as complicated parts such as a connecting rod, it is essential from the standpoint of costs that the alloy be worked by hot forging. At the same time, since the alloy inevitably suffers a given stress concentration during the working, the notch sensitivity should preferably be lower.
The existing alloys which have been hitherto studied and developed have not yet furnished all the characteristics which are practically essential. In this sense, the development of an alloy having well-balanced characteristic properties is very important and involves practical merits.